A bomb in eastern Afghanistan on Sunday killed six Nato service members, on a day where a total of 29 people died from roadside bombs and insurgent attacks.

Nato said the blast was caused by an improvised explosive device but provided no further details about the attack and did not identify the dead service members. The statement said Nato's policy is to allow "national authorities" to give details about the soldiers.

A surge in Afghan and coalition forces during the past two years routed Taliban fighters from many of their strongholds in the south, but the insurgents have stepped up their attacks this summer to take back key areas.

The service members' deaths were the latest on Sunday caused by bombs planted by insurgents along roadsides, paths or mountain tracks.

In addition to the six Nato deaths, bombs and attacks killed 16 Afghan civilians, five policemen and two members of the US-led coalition in southern Afghanistan, Afghan and Nato authorities said.

The civilians, including women and children, were killed in three blasts in Arghistan district, along Afghanistan's border with Pakistan.

Kandahar province spokesman Ahmad Jawed Faisal said one bomb exploded when a minivan ran over it Sunday morning. A second went off when other civilians riding a tractor arrived to help the wounded. A third explosion occurred about two hours later when a civilian vehicle hit a roadside bomb in another area of the district, killing two women.

At least 10 civilians were injured in the three blasts.

According to the United Nations, last year was the deadliest on record for civilians in the Afghan war, with 3,021 killed. The number of Afghan civilians killed dropped 36 percent in the first four months of this year compared with last year, but the U.N. says that too many are still being caught up in violence.

The policemen were killed while responding to a gun battle against insurgents early Sunday at a checkpoint in the Musa Qala district of neighboring Helmand province.

Daoud Ahmadi, the spokesman in Helmand, said a group of Taliban fighters attacked the police checkpoint at about 3 am. Afghan police called for reinforcements, but on the way, one of the police vehicles hit a roadside bomb, killing the five policemen.

Ahmadi said three other policemen were wounded in the four-hour gun battle against the insurgents. He says the bodies of 20 insurgents were recovered from the battlefield.

Separately, two Nato service members were killed in southern Afghanistan one in a roadside bomb explosion on Saturday and the other during an insurgent attack on Sunday.

Nato did not disclose where the incidents occurred or provide the nationalities of the soldiers killed.

So far this year, more than 225 NATO service members have been killed in Afghanistan.